Digital Microfluidic Systems for Self-cleaning Surfaces and Lab-on-Chip Devices Using Anisotropic Ratchet Conveyors

Abstract

This work focuses on creating active self-cleaning surface systems and lab-on-chip devices using anisotropic ratchet conveyors (ARCs). ARCs create micro-sized hydrophilic patterns on a hydrophobic background. Two different ARC systems were designed and fabricated with self-assembled monolayers (SAMs) and hydrophobic Cytop thin films. A Parylene C stencil mask process was developed to create patterns on the Cytop thin films without degrading the Cytop original hydrophobicity. Optical transmission measurements showed Cytop could improve glass substrate optical transmittance by 2.5~3.5% over the entire visible wavelength range. We first developed an active self-cleaning surface system using orthogonal vibration to drive the water droplet transport along the solar module surface with the assistance of ARC. Real-time demonstrations of droplet transport and surface cleaning were performed, in which the solar modules achieved a 23 percentage-point gain after cleaning. We then developed a platform using electrowetting-on-dielectric (EWOD) and liquid dielectrophoresis (L-DEP) with the assistance of ARCs. Droplet transport on an inclined surface to remove the surface contaminants and fog were demonstrated. In the end, we combined ARCs with surface an acoustic wave nebulization (SAWN) platform to create an integrated lab-on-chip device. The SAWN-ARC device integrated droplet delivery, merging, mixing, and nebulization functionalities. Mass spectrometry (MS) measurements with the SAWN chip were performed under different input frequencies. The SAWN transducer provided a controllable nebulization rate by varying the input nebulization frequency while maintaining a reasonable signal to noise ratio for MS detection.